CRISP Autofocus System

Applied Scientific Instrumentation Inc.

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The Continuous Reflection Interface Sampling and Positioning system (CRISP) is designed to maintain focus over time, i.e., to compensate for thermal and other factors that may cause the sample to drift out of focus over time. It also can be used to maintain a given focal point while scanning the sample in XY.

The CRISP system projects the image of a mask illuminated with an infrared LED into the sample plane. Only one half of the objective pupil is illuminated. This means that the point spread function of the objective is highly skewed, so that the reflected image of the mask will move laterally as focus is changed. CRISP detects this lateral motion of the LED image to obtain a focus error that is used to close the focus positioning loop.

The CRISP is usually installed with an ASI Dual C-Mount Splitter (DCMS) that contains the required dichroic beam combiner and blocking filters and allows the CRISP unit and camera to be used simultaneously on most common microscopes. The CRISP is automatically controlled, it maintains ideal focus for days, works with most normal microscope objectives, and integrates with ASI Piezo Z or motorized focus stages. The CRISP low-noise electronics allows locking to glass/water interfaces with a simple post-lock fine adjustment of focus.

The CRISP substantially eliminates focus drift in high-power microscopy applications by sensing minute changes between the objective lens and the sample’s cover slip. It also allows a sample to remain accurately focused for hours at a time with an accuracy of 5% of the objective depth of focus.

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